Here's my complete fan theory:
1939 - While Marion and her toddler Henry III listen to WBN in Chicago, station employees Roger and Penny Henderson reconcile (Radioland Murders). Meanwhile in New York, Indy and Sophia Hapgood depart to learn the Fate of Atlantis, but soon after part ways.
1947 - Sophia has married Bob Bolander (Saucer Men from Mars) and has a redheaded toddler, Steve. They join the newly formed CIA and head to New Mexico to investigate the Roswell incident. Sophia suggests Indy for the investigation, while Bob suggests Alex Tremulis, USAF, straight from the premiere of the Tucker Sedan he designed. Indy and Tremulis meet briefly but are soon dismissed. (Tremulis swears he never saw a flying saucer but popularizes the
design.) Sophia follows Indy to Utah and enlists his help finding and assembling the Infernal Machine in Babylon. Back in New Mexico, Bob is killed by contact with recovered alien technology.
1962 - Sophia has left the CIA and taken Steve to Modesto, California, also home to Roger and Penny Henderson with their children Curt, Laurie and Andy. Steve Bolander plans to attend Marshall College on Sophia's encouragement, and in turn has convinced his girlfriend Laurie's brother Curt to do the same. Ultimately only Curt flies east to Indy's school, while Steve marries Laurie and becomes an insurance agent (not a bad gig if your mother's really psychic).
...and I'm sure Indy crosses paths with the Red Tails in WWII, there's just nothing to work with there yet.